Flow control valves are well known in irrigation systems. Such valves control the flow or passage of water through an upstream pipe and thereby turn sprinklers fed by the pipe on and off. Such valves are often remotely controlled by control signals sent from an automated irrigation controller. For example, the controller often sends an electric actuating signal to a solenoid that is part of the valve to open the valve.
Certain known flow control valves have upstream fluid pressure on both sides of the valve member when the valve is closed. When the solenoid is actuated, the fluid pressure in a pressure chamber on one side of the valve member is exhausted or relieved. The upstream fluid pressure is then free to act on the other side of the valve member to disengage the valve member from the valve seat to open the valve. When the solenoid closes, upstream fluid pressure is then metered back into the pressure chamber through a metering path to restore the pressure balance across the valve member. This causes the valve member to reengage against the valve seat to close the valve. U.S. Pat. No. 6,263,901 to Lohde et al., which is assigned to the assignee of this invention, discloses a valve of this type.
In known flow control valves, the rate of flow into the pressure chamber through the metering path is what determines how quickly the valve closes. It is known in the art that the metering path can be sized to provide a particular closure rate. However, once this is done, the valve thereafter closes at that rate, subject to the caveat that the pressure differential across the valve member affects the closing rate as well. However, for a given design pressure differential across the valve member, a particularly sized metering path will provide a single valve closing speed.
Certain irrigation applications would ideally utilize flow control valves having different closing speeds. For example, in commercial turf applications, the flow control valve is typically open for an irrigation cycle lasting from 30 to 60 minutes. A standard valve used in such an application might take 20 seconds or so to close after the solenoid reseats. However, 20 seconds is only a small part of the irrigation cycle time, i.e. only about 0.5 to 1.0% of the total cycle time, so that such a valve closing speed is acceptable.
On the other hand, in other irrigation applications, such as greenhouse, nursery or small scale agricultural applications, a typical irrigation cycle might be much shorter. Sometimes a desired irrigation cycle might last only 30 to 60 seconds instead of 30 to 60 minutes. A valve closure time of 20 seconds then becomes an unacceptably large portion of the entire irrigation cycle. It would be desirable to have a valve that would close much more quickly than a standard valve for use in these applications.
Separate valves could be manufactured and provided having different closing rates. However, this requires different valve models and requires the retailer and installer of the valves to have the separate models on hand for use in all prospective applications. It also requires the installer to install the correct valve required for each application. There is a need in the art for a flow control valve having a plurality of closing rates with one rate being selectively chosen by the user in one application and another rate being chosen by the user in another application. However, prior to this invention, such a flow control valve was neither known nor available in the art.